This disclosure relates to a method and apparatus and in particular but not exclusively to methods and apparatus for use with time division duplexing carrier aggregation.
A communication system can be seen as a facility that enables communication sessions between two or more nodes such as fixed or mobile devices, machine-type terminals, access nodes such as base stations, servers and so on. A communication system and compatible communicating entities typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standards, specifications and related protocols can define the manner how devices shall communicate, how various aspects of communications shall be implemented and how devices for use in the system shall be configured.
A user can access the communication system by means of an appropriate communication device. A communication device of a user is often referred to as user equipment (UE) or terminal. A communication device is provided with an appropriate signal receiving and transmitting arrangement for enabling communications with other parties. Typically a device such as a user equipment is used for enabling receiving and transmission of communications such as speech and content data.
Communications can be carried on wireless carriers. Examples of wireless systems include public land mobile networks (PLMN) such as cellular networks, satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). In wireless systems a communication device provides a transceiver station that can communicate with another communication device such as e.g. a base station of an access network and/or another user equipment. The two directions of communications between a base station and communication devices of users have been conventionally referred to as downlink and uplink. Downlink (DL) can be understood as the direction from the base station to the communication device and uplink (UL) the direction from the communication device to the base station.
Some systems use FDD (frequency division duplexing) and other systems use TDD (time division duplexing). With FDD, different frequencies are used for UL and DL communications with a UE. With TDD, the same frequency is used for UL and DL communications but different time slots are allocated for UL and DL communication.
Carrier aggregation has been proposed and this allows the bandwidth associated with a UE to be expanded by concurrently using radio resources across two or more carriers. The component carriers are aggregated to form a larger overall transmission bandwidth
Control information may be communicated for example on a physical uplink control channel (PUCCH). For example, signalling for the purposes of error detection and/or correction may be provided by means of such signalling. Requests for retransmission of any information that the recipient node did not successfully receive are possible. For example, hybrid automatic repeat request (HARQ) error control mechanism may be used for this purpose. The error control mechanism can be implemented such that a transmitting device shall receive either a positive or a negative acknowledgement (ACK/NACK; A/N) or other indication regarding its transmission from a receiving device.
UL control information may be communicated on a physical uplink shared channel (PUSCH) if the PUSCH is scheduled for UL data transmission.
HARQ can be used in the context of carrier aggregation (CA). As mentioned previously, in carrier aggregation more than one carrier can be used for communications between two devices. HARQ feedback for one carrier may be transmitted on the Physical Uplink Control Channel (PUCCH) of another carrier.
Inter band TDD (time division duplex) CA with different UL DL configurations on the different bands has been proposed. This may cause complexities with respect to HARQ feedback because HARQ timing in TDD is coupled to the UL/DL configuration.